Adhesive composition for adhering printing plates to impression cylinders for flexographic printing

Abstract

Pressure-sensitive adhesive composition, having at least one polymer component formed of a monomer mixture of at least (a) one acrylic ester and/or methacrylic ester of the formula CH 2 ═C(R 1 )(COOR 2 ), where R 1 ═H and R 2 is a linear alkyl radical with 2 to 10 C atoms or a branched alkyl radical with at least 4 C atoms, (b) at least one N-alkyl substituted acrylamide, (c) at least one acrylic ester and/or methacrylic ester of the formula CH 2 ═C(R 3 )(COOR 4 ), where R 3 ═H or CH 3 and R 4 is a linear alky radical with at least 12 C atoms, (d) acrylic acid and/or methacrylic acid.

The invention claimed is: 
     
       1. A pressure-sensitive adhesive having at least one polymer component based on a monomer mixture comprising at least the following monomers:
 ia) 50 to 89.5 wt % of at least one acrylic ester and/or methacrylic ester having the following formula:
   CH 2 ═C(R 1 )(COOR 2 ),
 
 where 
 R 1 ═H and R 2  is a linear alkyl radical having 2 to 10 C atoms or a branched, noncyclic alkyl radical having at least 4 C atoms 
 and/or 
 R 1 ═CH 3  and R 2  is a linear alkyl radical having 8 to 10 C atoms or a branched, noncyclic alkyl radical having at least 10 C atoms, 
 
 ib) 5 to 20 wt % of at least one N-alkyl-substituted acrylamide, 
 ic) 5 to 25 wt % of at least one acrylic ester and/or methacrylic ester having the following formula:
   CH 2 ═C(R 3 )(COOR 4 ),
 
 where 
 R 3 ═H or CH 3  and R 4  is a linear alkyl radical having at least 12 C atoms, 
 
 id) 0.5 to 5 wt % of acrylic acid and/or methacrylic acid,
 the amounts being based in each case on the monomer mixture. 
 
 
     
     
       2. The pressure-sensitive adhesive as claimed in  claim 1 , wherein said at least one N-alkyl-substituted acrylamide comprises N-butylacrylamide, N-sec-butylacrylamide, N-tert-butylacrylamide, N-isopropylacrylamide, N,N-diisopropylacrylamide, N,N-dibutylacrylamide, N,N-dimethylacrylamide and/or N,N-diethylacrylamide. 
     
     
       3. The pressure-sensitive adhesive of  claim 1 , wherein said acrylic ester and/or methacrylic ester of the formula CH 2 ═C(R 3 )(COOR 4 ) where R 4  is a linear alkyl radical having at least 12 C atoms comprises stearyl acrylate and/or stearyl methacrylate. 
     
     
       4. The pressure-sensitive adhesive of  claim 1 , wherein said monomer mixture comprises more than 99 wt % monomers ia) to id). 
     
     
       5. The pressure-sensitive adhesive of  claim 1 , wherein the polymer component of the pressure-sensitive adhesive is based on a monomer mixture which, in addition to the monomers ia) to id), further comprises up to 10 wt %, based on the monomer mixture, of
 ii) additional copolymerizable monomers. 
 
     
     
       6. The pressure-sensitive adhesive as claimed in  claim 5 , wherein said additional copolymerizable monomers ii) comprise wholly or partly those having at least one singly or multiply unsaturated carbon-carbon bond and/or wholly or partly those having at least one singly or multiply unsaturated carbon-heteroatom bond. 
     
     
       7. The pressure-sensitive adhesive of  claim 1 , wherein the polymer component or components based on monomer mixtures comprising the monomers ia) to id) make up at least 90 wt % of the pressure-sensitive adhesive. 
     
     
       8. The pressure-sensitive adhesive of  claim 1 , comprising
 no tackifying resins, thermoplastic resins or reactive resins. 
 
     
     
       9. The pressure-sensitive adhesive of  claim 1 ,
 in crosslinked form, wherein the state of crosslinking corresponds to a micro-shear travel with respect of the shearing in 15 minutes of a sheet section initially measuring 13 mm×10 mm with a thickness corresponding to a basis weight of 50 g/m 2  under a load of 1.0 N in the direction of the greater longitudinal extent at 40° C., of between 100 μm and 300 μm. 
 
     
     
       10. A method for producing a crosslinked pressure-sensitive adhesive of  claim 1 , which comprises preparing a polymer component by radical polymerization from a monomer mixture comprising the monomers ia) to id), adding at least one thermal crosslinker during or after the polymerization, optionally mixing the polymer component with further polymer components based on a monomer mixture comprising the monomers ia) to id) and/or optionally further additives, and crosslinking the pressure-sensitive adhesive mixed with the crosslinker by supply of thermal energy to an extent that its state of crosslinking corresponds to a micro-shear travel with respect to the shearing in 15 minutes of a sheet section initially measuring 13 mm×10 mm with a thickness corresponding to a basis weight of 50 g/m 2  under a load of 1.0 N in the direction of the greater longitudinal extent at 40° C. of between 100 μm and 300 μm. 
     
     
       11. The method of  claim 10 , wherein said thermal crosslinkers comprise covalently reacting crosslinkers selected from the group consisting of epoxides, isocyanates and aziridines, and/or metal chelates. 
     
     
       12. The method as claimed in  claim 11 , wherein said crosslinker comprises N,N,N′,N′-tetrakis(oxiranylmethyl)-1,3-benzenedimethanamine in an amount of 0.03 to 0.1 part by weight, based on 100 parts by weight of the polymer component (solvent-free). 
     
     
       13. A method for bonding flexible printing plates to curved surfaces, which comprises bonding said flexible printing plates to said curved surfaces with a pressure-sensitive adhesive of  claim 1 . 
     
     
       14. A method for bonding flexible printing plates to curved surfaces, which comprises bonding said flexible printing plates to said curved surfaces with a crosslinked pressure-sensitive adhesive produced by the method of  claim 10 .